The chlorohydrin process for production of propylene oxide involves, in essence, a two-stage process. In the first stage, propylene chlorohydrin is formed from propylene and chlorine in excess water. The resulting dilute solution is then subjected in the second stage to treatment with a base such as lime or caustic soda in a hydrolyzer system to produce crude propylene oxide and an effluent water stream containing calcium chloride or sodium chloride. An excess of water is used in the first stage reaction in order to minimize by-product propylene dichloride and ether formation. Thus in practice, a relatively large throughput of water is involved in the overall process, and this necessitates treatment and disposal of a relatively large quantity of water effluent.
The majority of aqueous systems, in general, contain dissolved salts which may be converted to insoluble salts and deposited as scale on surfaces in contact with the water or aqueous system. If the system is at elevated pH and/or elevated temperature, the problem of scale formation can be magnified by the precipitation of soluble salts. In the chlorohydrin process, temperatures above 85.degree. C. and pH above 12 are required for optimum yields. Therefore, the process water which acts as a carrier for chlorohydrin and propylene must either be pretreated to remove or reduce calcium to eliminate potential scaling, or treated with scale inhibitors to reduce or eliminate scale formation. Pretreatment with zeolite units or with reverse osmosis units has been successful in removing calcium from the process water, but such units are expensive to install and operate. Prior attempts to include blends of polymer (including polyacrylates) and phosphonates have proved partially successful, and in practice it has been deemed necessary to use the combination of the polymer with the phosphonates despite the fact that the resultant phosphorus content in the effluent water is an undesirable constituent from an environmental standpoint.